Preheat oven to 375 degrees Fahrenheit; place 2 sheet pans inside oven as it preheats.
Spread about half a tablespoon of butter on one side of each of the four pieces of bread.
Spread a thin layer of Boursin cheese on the other side of each piece of bread (opposite the buttered side).
Assemble sandwiches on hot sheet pan - bread buttered side down followed by two slices of cheese followed by bread buttered side up.
Place second hot sheet pan on top of sandwiches like a panini press.
Bake sandwiches 8-12 minutes, depending on desired brownness. (Feel free to lift pan to check on top, but know that bottom of sandwiches will be significantly more brown).